The present invention relates generally to drive means for work transfer apparatus and more particularly to improved dual cam drives for effecting cyclical advancement of work transfer apparatus between successive work stations.
Multiple cam drive assemblies have long been in use in conjunction with various types of work transfer apparatus including linear, rotary and reciprocating type apparatus. However, in both the linear and rotary types of drive arrangements it has been necessary to position the two cams on separate shafts positioned in side-by-side substantially parallel relationship with respective cam followers positioned on the work supporting transfer in laterally or radially offset spaced relationship. While these drives perform satisfactorily, this dual shaft side-by-side cam arrangement makes them more expensive to construct because timing means must be provided to insure proper rotation of each of the respective cams with respect to the other as well as the need for multiple bearings and shafts. The presence of such timing means not only increases the cost of manufacturing the associated drive means but also increases the cost of maintenance as well as the potential downtime due to the presence of additional operating apparatus. Further, because precise timing of the two cams is critical for operation thereof, additional time will be required by maintenance personnel to reset and verify proper timing subsequent to any maintenance or repair requiring dismantling thereof. Therefore, in order to eliminate the need for this additional timing mechanism and reduce the attendant maintenance time and costs, it is desirable to locate both cams on a single shaft and to align the cam followers accordingly.
Multiple cams on a single shaft have been previously utilized although such use has been restricted to reciprocating drive apparatus wherein dual primary cams are provided on opposite ends of the reciprocating work supporting apparatus. Secondary cam followers can then be provided therebetween which will engage only a center secondary cam. However, because the primary cam followers never enter the area occupied by the secondary cam there has not been any need to be concerned with possible interference between the primary and secondary cam followers and the primary and secondary cams. It is generally not practical to utilize a single cam as the cam must include provisions for both acceleration/deceleration of the work transfer apparatus as well as a constant velocity movement thereof. While for very short stroke reciprocating or linear transfer operations it may be possible to omit the constant velocity portion and thereby employ only a single cam having acceleration/deceleration portions, this would be totally impractical for the transfer distances generally required in commercial applications because the barrel cam would become excessively long thereby substantially increasing the cost of the apparatus.
The present invention, however, overcomes these disadvantages in providing primary and secondary cams rotatably supported on a common shaft thereby totally eliminating the need for additional and potential complex timing gear means or the like and without unnecessarily increasing the required length of the cams. The primary and secondary cams may be fabricated as a single integral unit although it is believed preferable to separately fabricate same for both cost and ease of replacement. The elimination of timing means not only substantially reduces the complexity of the overall drive system but offers improved reliability due to the reduced number of operating parts. Additionally, significant reduction in downtime may be realized by use of the subject drive system as not only is the amount of apparatus requiring maintenance and/or repair reduced, but there is no need for resetting of such potentially complex timing means as was heretofore required. Thus, the subject invention provides an improved drive system which is well suited for use in rotational, linear and reciprocating indexing of work transfer apparatus.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.